All infants have a decline in hemoglobin(Hgb) after birth because of increasing PaO2 and Hgb saturation after birth. In very low birth weight (VLBW) infants (birth weight ,1500 g), the nadir at 1 to 3 months after birth is lower than in term infants because of (1) greater phlebotomy losses for blood tests, (2) shortened red blood cell survival, and (3)rapid growth.